The card says "you cannot perform another attack this round," which leads me to believe that it's supposed to be fitted on lower PS ships, so it can be used towards the bottom of the pile.

Obviously it's not talking about the ship it's placed on, because when it came out ships that could fire twice didn't exist yet (even now there's only one, and he can't take gunner)

Anybody else know what's going on here? Surely I'm not the only person to notice.

Just posted this yesterday in a thread in the rules question section asking something similar

Originally it was to prevent you from triggering gunner off of a gunner attack. I shoot-miss, gunner-miss, gunner again-miss, gunner a third time, and so on.

Since then there are cluster missiles, Coran Horn, huge ships with multiple weapons...

Most of the time though it isn't relevant. It is just a special clause to avoid some corner cases that might break the game.

So, yeah. It only effects the ship it is on. Any time a card says "you" it is referring exclusively to the ship, not the player. That us one of those definitional rules in the beginning if the rulebook that are easy to miss.

Oh ok, so it's even impossible or to go with two gunners and chain them together. Not that that's a viable thing to do anyway.

Correct, but all your other ships are free to continue attacking for the rest oft the round

Gunner, and crewman Luke, prevent the ship they are on from making any additional attacks. After all, they ARE giving their own ship an additional attack although you must miss with the first attack to get the second. They do NOTHING to other ships in your squadron.

Oh, some ships HAVE been able to make two attacks in a single round for a long time. Cluster Missiles allow for two attacks. If you want to get complicated a ship with a Gunner, or Luke, firing a Cluster Missile could make three separate attacks. It would get to make two with the Cluster Missile and if the LAST one of those misses, you do them one at a time, that would then trigger a primary weapon attack via Gunner; Gunner could trigger if the first missile misses but then the second DOES NOT HAPPEN as the Gunner text kicks in and prevents any additional attacks.